Various types of carbon black that differ in properties are used for rubber reinforcement applications. Since the properties of the carbon black are major factors that determine the performance of the resulting rubber, carbon black having properties suitable for the target application is selected and added to a rubber composition.
For example, high-structure hard carbon black having a small primary particle size and a large specific surface area (e.g., SAF (N110) or ISAF (N220)) is used for a rubber member (e.g., tire tread) for which high abrasion resistance is required. However, a rubber obtained using a rubber composition that includes high-structure hard carbon black is highly reinforced, but tends to exhibit high heat buildup.
In recent years, development of fuel-efficient tires has been increasingly desired in order to address a social need for saving resources and energy, and a rubber composition that achieves low heat buildup suitable for fuel-efficient tires has been extensively developed. Low heat buildup is normally achieved by adding carbon black having a large particle size (i.e., equivalent diameter of secondary particles formed by aggregation and fusion of primary particles) and a small specific surface area to a rubber composition.
A rubber that is highly reinforced and exhibits low beat buildup is required to produce the tread of fuel-efficient tires. However, since carbon black that is used to improve the degree of reinforcement and carbon black that is used to improve heat buildup completely differ in particle size and specific surface area (i.e., have a trade-off relationship), it is difficult to obtain the desired rubber composition by adjusting the particle size and the specific surface area of the carbon black.
In order to deal with the above problem, technology has been proposed that improves rubber properties (e.g., degree of reinforcement and heat buildup) by microscopically evaluating the colloidal properties of carbon black in addition to the particle size, the specific surface area, the structure, and the like (that have been regarded as important as the basic properties of carbon black used for rubber reinforcement applications), and adding carbon black that has specific properties to a rubber component (see Patent Literature 1 (JP-A-2002-188022), for example).